1. Field of the Invention
The present invention relates to a force sensor that includes a base unit, an elastic supporting unit connected to the base unit, and an action unit supported by the elastic supporting unit, and detects at least one of an external force acting on the action unit and a moment acting on the action unit. The present invention also relates to an industrial robot including the force sensor.
2. Description of the Related Art
Existing types of force sensors for detecting an external force include a strain gauge type (resistance type), a capacitance type, and an optical type. Among the three types, the strain gauge type (Japanese Patent Laid-Open No. 10-274573) is most commonly used.
Examples of existing optical type image sensors include an optical sensor using a technique of tracking control and focus control employed in information recording and reproduction apparatuses such as optical disc drives (Japanese Patent Laid-Open No. 2005-241353) and an optical sensor using a light source and a four-element photodiode (PD) (Japanese Patent Laid-Open No. 2005-98964).
Main uses of a force sensor include that for an arm or a finger of an industrial robot. Because higher precision has been required for an operation performed by an industrial robot, a force sensor capable of detecting a force with higher precision and higher sensitivity has been needed. Moreover, because the arm and the finger of the robot have to move rapidly, control with a higher bandwidth is necessary. Although a higher rigidity is required for the force sensor in this case, in general, the detection sensitivity of a force sensor decreases when the rigidity is increased.
However, it is difficult to obtain both a high rigidity and a high detection sensitivity with the force sensors described in Japanese Patent Laid-Open Nos. 10-274573, 2005-241353, and 2005-98964, because the resolution of a displacement sensor, which detects a displacement that is required to calculate an external force and the like, is low and the detection sensitivity of the displacement sensor is insufficient.